Silicon-germanium resistor and method of making it



May 15, 1951 J. R. FISHER ETAL 2,552.,626

SILICON-GERMANIUM RESISTOR AND METHOD OF MAKING IT Filed Feb. 17, 1948 2 Sheets-Sheet 1 /NVENTORS ATTORNEY May 15, '1951 J. R. FISHER ET AL 5 5 SILICON-GERMANIUM RESISTOR 'AND METHOD OF MAKING IT Filed Feb. 7, 94s 2 Sheets-Shet 2 vF/G..4.

J. R. F ISHE R em JNl/ENTORS .G. K. TEA L Patented May 15, 1951 SILICON-GERMANIUM RESISTOR AND METHOD OF MAKING IT Joseph R. Fisher, Chatham, and Gordon K. Teal,

Summt, N. J., assignors to Bell Telephone Laborato'es, Incorporated, New York, N. Y., a corporation of New York Application February 17, 1948, Serial No. 8,884

i Claims. l

This invention relates to resisto's and more particularly to resistors comprising a film of mixed silicon and germanium and to methods of making such resistors.

Resistors having a relatively high 'esistance may be made by depositing a thin film of conductive material on an insulating hacking. If an extremely high resistance is required, a film material of high resistivity may be used. The making of such resistors often involves obtaining a suitable temperature coeficient of resistance along with a desired resistance value. In general, film materials of relatively high conductivity have low resistance-temperature coefiicients and those of relatively high resistivity have high resistancetemperature coeicients. For some applications it is necessary to use film materials of high resistivity in order to obtain a suitable resistance value, but the requirements are such that a low resistance-temperature coefficient i desired.

One object of this invention is to produce a film type resistor having reiatively high resistance and a relatively low temperature coecient of resistance.

A feature of this invention resides in employing a film of mixed silicon and germanium on an insulating backing to produce a resistor of the type desired.

Another feature of this invention lies in codepositing the two materials so that a homogeneou film of a desired characteristic results.

In one embodiment of this invention, a relatively small ceramic tube, such as a porcelain tube is provided with a film of mixed silicon and germanium of very high purity, preferably by the pyrolytic deposition of the materials from a gaseous mixture of their tetrachloride in hydrogen. The deposition occurs when the hydrogen-ehloride mixture is passed over the surface oi the heated ceramic tube in a reaction chamber. A good deposit may be obtained with a ceramic tube temperature between 950 and 1150 C. The ceramic tube may be heated by a tantalum wire passing through the bore OI" the tube.

Other and further objects and features of this invention will appear more iully and clearly from the following description of exemplary embodiments thereof taken in connection with the appended drawings in which:

Fig. 1 is a View in elevation of a resistor made in accordance with this invention;

Fig. 2 is a perspective View of another resistor made in accordance with this invention and includes a supporting element used in the manufacture of the resistor;

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Fig. 3 is a sectional View of a portion of a resistor such as those oi Figs. 1 and 2, enlarged to show details of the Construction; and

Fig. 4 is a diagram of apparatus which may be used in producing resistance films in accordance with this invention.

The resistor shown in Fig. 1 comprises a tube Hi of insulating material such as a suitable ceramic, having a film i I of resistance material applied theret-o. Contact is made to the resistance film Il by terminals 12. The film Il as shown is in spiral form to provide a long path between the terminals i2.

The resistor shown in Fig. 2 is similar to that shown in Fig. 1 except that the film covers all of the surface from terminal to terminal. The insulating tube 26 is completely cove-red With a film Zi of resistance material and provided with terminals 22. The element 23 forms no part of the finished resistor, but merely provides support for the resistor during processing. The loops 24 are for connecting 'the support 23 to other parts of the processing apparatus later to be described.

Fig. 3 shows more specifically the Construction of one end of these resistors. The tube 20 is coated on its outer surface with the film 2! by a process to be described and a terminal 22 is applied to each end portion of the film Zl. The terminals 22 may comprise a film of heat cured metallic paste such as a paste of nely divided silver and a uxing material such as a glass with suicient temporary hinder and solvent to make the paste workable.

Films of mixed silicon and germanium may be deposited on the surfaces of ceramic tubes by means of the apparatus illustrated in Fig. l. The ceramic tube 25 mounted on the wire 23, which may be of tantalum, is Suspended by the loops 24 in a reaction chamber 39. The chamber 30 is provided with a suitable cover 3| which may be attached by a screw thread. Mounted on the cover and Secured in sealing relation therethrough are support and terminal elements or tubes 32 and 33. The support elements 32 and 33 are made of Copper tubing or other similar material so that they may also serve a electrical conductors and may be cooled by suitable fluid passing through them. The support wire 23, which also serves as a heater, may be Secured to the elements 32 and by suitable resilient supparts such as the hook and spring assemblies 34 and 35.

The reaction chamber 3!) is provided with a cooling jacket 36- having entrance and exit ports 31 and 38 respectively. Inlet pipe i!) connected to one end of chamber 311 provides for the entrance of the various gaseous materials used in the deposition process. The Waste material from the chamber are exhausted through the outlet pipe M.

The gaseous materials used in this process are supplied from a nitrogen tani: or reservoir 42, a hydrogen tank or reservoir 43, a silicon tetrachloride boiler 44 and a germanium tetrachloride boiler 45. The nitrogen is used to fiush out the chamber initially and the other materials are mixed in the proper proportion to obtain the film or coating desired.

The nitrogen from tank 12 is admitted through valve 46 to a deoxidizing furnace il to remove any traces ol free oxygen in the gas. The cleoxidized gas is then passed through drying toWers 58 to remove any traces of water vapor. From the drying toWers the gas passes through a flow meter 49 and a valve 58 by way of pipe 55 and inlet to the chamber 35).

I-Iydrogen from tani: 33 passes through similar apparatus including the valve the deoxidizing urnace 53, the drying towers 5 3, pipe 55, flow meter valve 5?, pipe &8 to pipe 5! and then through inlet pipe l@ to the chamber The oxygen and moistu'e-free hydrogen also may be conducted by pipe Ed to the silicon tetrachloride and germanium tetrachloride boilers l i and respectively. Hydrogen passing to the silicon tetrachlorde boiler goes through ow meter valve 62, boiler i l, refiux condenser 53, valve 54, ppe 55 to the pipe iii and thence through the inlet pipe i@ to the chamber Sii. The hydrogen for the germanium tetrachloride boiler goes from pipe BD through the flow meter 65, Valve Bl, boiler 35, reflux condenser 58, valve 69, pipe 5l, and inlet pipe 49 to the chamber 39.

The silicon tetraohloride and gernanium tetrachloride boilers M and 45 are provided respectively with heaters ?i and 'J2 for boiling off their respective vapors.

The condenser 83 receives cooling water from a supply ?3, through a heater M, and a temperature indicator ?5. cooling water upon leaving condenser 53 passes through another heater 16, a temperature indicator Ti, a tube '18, through the support tube 32 in the chamber se and thence through the support tube 33 by way of the tube '19. Cooling water leaving tube 33 passes through tube 89, inlet Bl' to cooling chamber and thenoe out through the exit port 38. The tubes ?8, ?9 and sa are of an insulating material such as rub'ber or the like for reasons which will appear upon further description. The condenser &S may be provided with a separate source of cooling water from the reservoir 8! through the heater 32 and temperature indicator This water is exhausted through the outlet or exhaust pipe se.

The support and heating wire 23 in the chamber 36 is heated by electric current *from the source 85. The circuit is through a suitable regulator 85 by way of closed switch 87, transformer 88, to the support and cooling tubes 32 and 33 and by way of the resilient support means 3 and 35 respectively to wire 23. As previously noted the tubes 18, 'm and se are of insulating material. This is to confine the electrical current to the metallic tubing within the chamber 30.

A typical deposition of mixed silicon and germanium on the ceramic tube an may be as follows: The valve E@ is opened and the reaction chamber 3% is fiushed with nitrogen. After sufficient fiushing, the valve E@ is closed and the valve 57 is opened allowing dry, oxygen-free hydrogen to flow through the reaction chamber. While the hyclrogen is fioWing through the 'eaction chamber, the switch El? is closed and the wire 23 is raised to a temperature suificient to heat the ceramic tube 29- to 1200 C. at which temperature it is maintained for about 30 seconds. The temperature of the tube 20 may be determined by any well-known means such as an optical pyrometer. The tube 28 is now ready to be covered with the silicon--germanium mixture, the thckness and character of the film being determined by the hydrogen fiow, the flow or" silicon tetrachloride and of germanium tetrachloride, the time of deposition, the temperature of the ceramic tube and the type of ceramic tube used. By suitably controlling these variables, a coherent, smooth film may be obtained on a ceramic base. successful clepositions have been made With germanium tetrachloride concentrations between 0.87 and 8.0 mol per cent relative to silicon tetrachloride.

Preparatory to effecting the deposition, the valves 54 and 39 are opened and the openings of vaives 5?, and fil are adjusted to give the desired ratio between. the amounts of hydrogen flowing through the tu'oe 58 and the amounts flowing through the 'boilers 34 and 45. The heaters M and 82 are adjusted to give a water temperature of about 3 C. and may be therrnostatically controlled. The heater '56 is adjusted to maintain. the water entel-ing the cooling system of the reaction chamher 38 at approximately room temperature say 25 C.

After several minutes of flow to establish the equilibrium of the gaseous mixture of hydrogen, silicon tetrachloride and germanium tetrachloride, the temperature of the ceramic tube 20 is rapidly raised to any desired temperature between about 950 C. and 1150 C. and maintained for the period of the deposition which may be 2 minutes at a temperature of 1100 C. During this period the gaseous tetrachlorides are decomposed thermally, the pure liherated silicon and germanium are deposited on the surface of the ceranic tube E@ and the unwanted products of the 'eaction are discharged through the outlet Gi.

If it is assumed that the hydrogen gas emerging from the boilers and 2:5 is highly saturated, possibly supersaturcced, with silicon tetrachloride and germanum tetrachlorde respectivcly, the conclensation oocurring within the condensers 63 and 58 will reduce the concentration of the chlorides to the saturation values corresponding to the temperatures within the condensers. Therefore, When the mixture enters the reaction chamber 353, it encounters a chamber wall temperature which is somewhat higher than that of the condensers. This diflerential increases the saturation pressure of the gaseous mixture to a point which is safely above the partial pressure of the ehlorides and therehy prevents condensation of the chlorides on the walls of the reaction chamber. The same diflerential temperature relation is maintained between the condenser and the terminal xtures 3:?. and 33 by the cooling water owing therethrough froni the heater 18.

After a suitable cleposition time has elapsed, the apparatus is shut down and the ceramic tube is removed. The germaniun-silicon film may be provided With Contacts as previously set forth with respect to Figs. 2 and If a longer film such illustrate in l is desired, the un- Wanted material may be ground off or otherwise u removed With suitable apparatus.

Although the invention has been disclosed by exemplary embodiments thereof, it is not intended that it be limited thereby but by the scope of the appended clams only.

What is claimed is:

1. A resistor comprising a ceramc support, a thin film on said support of a material consisting of a mixture of silicon and germanium, and spaced electrical connecting means Secured to said film, the germanum constituting from of the order of 2 to the order of 18 per cent by Weight of the film.

2. A resistor comprising a ceramic support, a thin film of mixed silicon and germanium on said. support, and spaced e1ectrica1 connecting means in contact With said film, the atomic ratio of silicon to germanium in said film being about 11 to 1.

3. An electrcal film resistor comprising an alloy of silicon and germanium, the germanium constituting of the order of 18 per cent by Weight of the film and means for supporting said film.

4. The method of making an electrcal resistor, which comprises simultaneously introducing silicon tetrachloride and germanium tetrachloride into a chamber having a body therein, the germanium tetrachloride concentration relative to silicon tetrachloride being betWeen substantially 0.87 and 8.0 mol per cent,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 97%,022 Hatfield Dec. 6, 1910 1,497,417 Weber June 10, 1924 1,739,256 Pender et al. Dec. 10, 1929 1964322 Hyde June 26, 1934 2,022,314 Heyroth et al Nov. 26, 1935 2,439,654 Gaiser Apr. 13, 1948 2,472,770 Helterline, Jr. June 7, 1949 OTHER REFERENCES Article by Teal et al., Journal of Applied Physics, Nov. 1946, pages 880, 881.

J aee et al., Technology of Germanium, Transactions of the Electrochemical Society, vol. 89, 1946, pages 277-289. 

1. A RESISTOR COMPRISING A CERAMIC SUPPORT, A THIN FILM ON SAID SUPPORT OF A MATERIAL CONSISTING OF A MIXTURE OF SILICON AND GERMANIUM, AND SPACED ELECTRICAL CONNECTING MEANS SECURED TO SAID FILM, THE GERMANIUM CONSTITUTING FROM OF THE ORDER OF 2 TO THE ORDER OF 18 PER CENT BY WEIGHT OF THE FILM. 